Advances in genomics, proteomics, combinatorial chemistry, and compound library management have each driven the need for increasingly fast, accurate methods of high throughput liquid sample handling. As information libraries broaden, so does the need to be able to conduct automated sample handling and screening in increasingly small volumes, including in nanoliter volumes. Researchers in biopharmaceutical and chemical companies, universities and other research institutions often seek automated research systems that significantly enhance productivity and improve other processes, such as drug discovery processes. Thus, cost-effective miniaturized screening essays, and related sample management, have assumed greater importance.
Several currently available technologies provide low-volume dispensing or delivery capability. Among others, these include “contact” and “noncontact” dispensing methodologies. Contact dispensing uses surface tension created by touching the dispensed droplet on the receiving substrate to remove the droplet from the dispensing apparatus.
Noncontact dispensing uses force or pressure, such as fluid or air pressure, to eject the droplet from the dispensing apparatus without contact first with the receiving substrate. Because dispensing can occur from the top of the well, plate processing times can be significantly faster when drops are dispensed serially “on-the-fly.” Often these technologies are applied to liquid dispensing or handling applications involving standard 96-well, 384-well, 1536-well, and increasingly dense microtiter plates or other substrates.
The current trend in the high throughput screening (“HTS”) market is to reduce the assay volume in order to reduce costs. This reduction is primarily accomplished with low volume, high-density microtiter plates such as 384-, 1536-, or 3456-well formats. As 1536-well and larger plates become more widely used for HTS applications, there is a need for practical, automated liquid handling solutions for both compound transfer and assay assembly.
As an example of one application, without limitation, compound libraries are being developed to store millions of potential drug compounds. Scientists must be able to not only store their compounds, but also to quickly retrieve and sample a single compound, thus demanding fast and accurate compound sampling.
Management of compound libraries often involves compound reformatting, whereby aliquots of samples in a liquid compound library are transferred from a “mother”plate onto another microtiter plate, the “daughter” plate, in which the user wishes to perform the test or assay. Because testing is increasingly performed on a smaller scale, there is a need to increase the density of sample plates. Thus, reformatting process may occur among “mother” and “daughter” plates of the same density, or among plates of different densities where samples from smaller-density plates are combined onto a larger density plates, as some examples, only, combining 96-well plates onto 384-well or 1536-well plates, and other permutations.
In addition, primary drug screening requires scientists to search through thousands of potential drug candidates to find out which ones show biological activity towards a target. The screening technology has progressed from a few 96-well plates and a few hundred interactions per year, to today's HTS. Techniques which enable researchers to perform complex, high volume experiments at a lower cost and in shorter time than traditional techniques facilitate faster and less expensive drug discovery.
In many cases, these processes are automated by combining incubators, centrifuges, plate readers, and aspirate and dispense robots together into a single platform, known as an integration robot. Each contributing component in the robot must operate efficiently, accurately, and with easy integration. Thus, an HTS robot can expect to present a 1536 well microtiter plate to the integration station, have all wells filled, and the plate removed in minutes, if not seconds.
Moreover, the sequencing of the human genome project has produced the fields of genomics and proteomics, which are global studies of an organism's gene and protein complements, respectively. A related field, structural genomics, has emerged which uses high throughput protein crystallography as its central platform to solve the structure for thousands of proteins.
In the past, protein crystallography has been a labor-intensive, low-throughput process. However, high-throughput protein crystallography involves using many automation concepts from HTS. The liquid handling requirements of protein crystallography are similar to those for HTS and include low sample volumes, high dispense speed (for example, to avoid evaporation of the mother liquor), and accurate dispense volumes.
Automated liquid handling apparatus perform a central role in such uses. By providing fast, accurate sample handling, such robots perform many types of laboratory functions, including as examples only, plate compressions or expansion from 96-, 384-, 1536- well or other microplates; plate replication and reformatting; reagent additions; and dilutions.
Technologies are currently available to perform automated liquid sample handling in light of the requirements for non-contact transfer of samples. Once such technology is the Hummingbird™ dispensing system (Cartesian Division of Genomic Solutions, Inc., Irvine, Calif.). The Hummingbird Technology is a robust, highly parallel solution for transferring compounds and creating assay plates for HTS, including the transfer of small volumes of liquids. This technology utilizes an array of capillaries to transfer very small nanoliter volumes of compounds, as desired.
The Hummingbird noncontact technology involves sipping or aspirating a sample from a source plate or other substrate using the capillary action of narrow-bore glass capillaries, followed by dispensing with a pulse of air. Sample transfer is accomplished by dipping an array of capillary tubes mounted in a mounting block into a source plate, filling the capillaries by capillary action, and dispensing into the destination plate or other substrate by applying pressure to the backside of the capillaries. The transfer volume is determined by the volume of the capillary tube.
The mounting block currently consists of an array of narrow-bore capillaries that are glued into a plastic plate. This allows for plate replication, plate duplication and plate reformatting, sample dilution and reagent addition. Hummingbirds can be operated in a standalone mode or via an ActiveX interface and configured with a robotic plate handler. in 96 or 384 well plates.
Such technologies allow for accurate, high-speed, non-contact, low volume aspirate and dispense systems, reagent addition and array printing, compound transfer, and assay assembly. However, the capillary tubes in the mounting blocks may become damaged or clogged, which can result in downtime. Moreover, because the capillary tubes are glued or molded fixedly in the mounting block, they are difficult to repair or replace. In addition, because the capillary tubes are fixed, it is challenging to adapt the current mounting block with glued or molded capillaries to applications where variability in sample size in a single microtiter plate may be desired.
Thus, there remains a need for improved apparatus and methods to overcome these drawbacks.